Power circuits for high-frequency electronic converters



May 25, 1948. J. L. BOYER 2,442,259

POWER CIRCUITS FOR HIGH-FREQUENCY ELECTRONIC CONVERTERS Filed Dec. 14, 1946 2 Sheets-Sheet J,

1 I INVENTOR 53am! John L. Boyer ATTORNEY May 25, 1948. Y J. L. BOYER 2,442,259

POWER CIRCUITS FOR HIGH-FREQUENCY ELECTRONIC CONVERTERS Filed Dec. 14, 1946 2 Sheets-Sheet 2 Fig. 2.

WITNESSES:

WWJJM INVENTOR Jol h L. Boyen ATTOR N EY Patented May 25, 1948- POWER CIRCUITS FOR HIGH-FREQUENCY ELECTRONIC CONVERTERS John L. Boyer, Wilkinsburg, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 14, 1946, Serial No. 716,197

12 Claims. 1

My invention relates to electronic frequencychangers or converters for converting directly from alternating current of one frequency to alternating current of a higher frequency. More particularly, my invention relates to high-frequency converters utilizing gas or vapor-filled tubes, whereby an output can be obtained, having a kilowatt rating which is greater than that which can be economically obtained with highvacuum tubes.

An important field of application of the invention is in supplying energy for an induction furnace requiring frequencies in the range of from 1000 to 2000 cycles per second, more or less. This is a frequency-range in which rotating motorgenerator sets have poor efficiency and poor regulating characteristics, and in which high-vacuun-tube oscillators can not be economically use The principal object of my present invention is to provide power-circuits for high-frequency electronic converters of the type which I have described, in which two groups of tubes are provided, each group having its anode-circuits connected to the several phases or conductors of the input-circuit, and having a separate cathode-bus, in combination with an output-transformer or reactor having a mid-tapped primary winding, the midpoint of which is connected, preferably through a reactor, to the neutral point or intermediate-voltage point of a power-transformer which is utilized in the input-circuit. The load or high-frequency output-circuit is connected to the output-transformer. A more particular object of my invention is to provide a commutating-capacitor, preferably shunt-connected across the rimary terminals of the output-transformer, in a combination such as I have described.

By means of my present invention, I have been able to achieve success, in a high-frequency electronic converting apparatus, Where other powercircuits have proved unsuitable.

. My present invention is applicable to gas-filled hot-cathode tubes, or to ignitrons. Suitable gasfilled hot-cathode tubes, in my high-frequency converter, will make it possible to obtain efficient operation in a frequency-range extending up to 3000 cycles, or more, in installations in which the power-requirements are not too high. Special ignitrons, in my high-frequency converter, will have a greater output-capacity, but in general can not, at. present, be operated at frequencies exceeding 1500 or 2000 cycles.

When my present invention is applied to ignitrons, it is preferably to utilize a special excitation-control circuit which constitutes the subject-matter of my concurrently filed copendin application Serial No. 716,196, filed December 14, 1946, although I am not altogether limited, in the present invention, to any particular excitation-control.

With the foregoing and other objects in View, my invention consists in the circuits, systems, methods, combinations and parts, hereinafter described and claimed, and illustrated in the accompanying drawings, wherein Figures 1 and 2 are simplified diagrammatic views illustrating the essential features of two different forms of embodiment of my invention, omitting known features of switches, voltage-regulators, and other like features which are not necessary to an understanding of the present invention.

In Figure 1, I show the fundamental features of the power-circuits and the excitation-circuits of a preferred form of embodiment of my invention, utilizing six ignitron-tubes, I through 6, which are supplied from a three-phase input-circuit l which is energized from a commercial-frequency power-transformer 8, having delta-connected primary windings 9, and zig-zag secondary windings [0 having a neutral point H. The primary windings 9 are energized from a threephase circuit l3, of cycles or other frequency. The secondary windings l0 energize the threephase input-circuit I of the ignitrons I to B.

The ignitrons are disposed in two groups, I, 2 and 3, and 4, 5 and 6, respectively. Each phase of the input-circuit l is connected to the anodecircuits M of two ignitrons, one in each group. The three cathode-circuits l5 of the tubes l, 2 and 3, in the first group, are connected to a common cathode-bus l6; while the three cathode-circuits l5 of the tubes 4, 5 and 6, of the other group, are connected to another common cathode-bus H.

In accordance with my present invention, a high-frequency load-circuit is connected to the two cathode-buses l6 and H, by means of an output-transformer or reactor 20 having a midtapped primary winding 2|, the mid-point 22 of which is connected to the neutral point i l of the secondary winding ID of the power-supply transformer 8, preferably through a direct-current reactor 23, which reduces the circulation of the high-frequency fundamental and harmonic currents in the supply-transformer 8, and also helps to reduce any pulsation in the high-frequency output-voltage wave.

The output-circuit 24 of the converter is shown 3 as being energized from a secondary winding 25 of the output-transformer 20, and it is shown as being connected to an induction furnace 26 which is symbolically represented by an inductance 21 and a resistance 28.

In most cases, it will be necessary to utilize a commutating-capacitor'30, for effecting the highfrequency commutation of the'output-currents of the converter, or for at least assisting in the commutation of such currents.

across the two cathode-buses l6 and llgthat is, across the primary terminals of the outputtransformer 20. A second capacitor-3-bier-powerfactor-correction purposes, is also commonly'connected across the terminals of the inductionfurnace load 26, that is, across, thesecondary terminals of the output-transformer 20.,

It is possible, of course, to omit either-one-of the capacitors 3B or 3|, and to utilize the remaining capacitor to' take over the functions lofwboth increasing the size of the remaining capacitor,

for this purpose. It isusually more-economical,

however, to utilize the capacitor 3 l to adjust the powerfactor of the'loadto near unity, and'to utilizethecapacitor: 30 solely for commutating purposes, for alternately charging, firstinone direction and then the other, during successive half-cycles of the output-frequency, cutting oil?v the output-current at the end 'of each outputfrequency half-cycle, thus extinguishingor come mutating, theload-currents flowing through 1 the mainanode-cathodecircuits of the-several tubes.

I to'ELaccording to whichever tube isncarrying current at the-moment.

As more par-ticularly'described and=claimed inmy copending -application, aspeeial excitation-- circuit is utilizedforthe converter-tubes: I to 6.

Eachtube, in addition-to its anode-circuit l4 andcathode-circu-it I5, is-provide'd-with a controlor shielded grid' 33*; ill-01056137 spaced relation-withrespectto the anode, an eXcitatio-n grid- 84 in closely I spaced relation to the control grid,

an ignitor '35, and an'auXilia-ry'anode or electrode- 3t. A'tinycircle or dot 3l has-been placed withinthe diagrammaticrepresentation =of= eachtube,

as a convention "for-indicating the presence of. a gasor-vapor, or other-means fortcausin the ig-e nitor'" or--other' control-electrode of the tube-to become ineffective; in-general; to stop-the firing of the-tube,-once the' firing hasbeerr initiatedh The outer grid '34 --ac-ts=-as adeionizing surface forthe-inner controlgrid 33. The spacings between-the inner grid-and theanode,- and between the two grids, should be assmall as is mechani cally possible, usuallyabout-one-quarterof an inch; The'grids should be thin with small-holes therein; usually about one-eighth toone-quarter of aninch in diameter.- Bythese expedients, the

grids are made more effective to control the tubes at a high-frequency rate.

The exciting currents for the several ignitors 35, 01? the tubes I to figare-suppliedby a'set of threesingle-phase firing ci-rcuitexcitation-traine formers 4il-,-and six ignitor-coupling insulating-- transformers 4b.

As more particularly describedandclaimed in my copendingapplication, thenumberf ig-- nitor-misfires may be reducedgxby connecting the ignitor-coupling transformers 4 4lin series in pairs, so as to fire the-two-ig-nitors which should fire at the same time. The series connection has the advantage that, when one: of the two ignitors does not fire as soon as the other, a.double voltage is impressed upon the hard-firingignitor.

As shown in Fig; 1, the commutating-capacitor 30 is: connected The series ignitor-firing effect can be obtained in a number of different ways, as by means of a mid-tapped balancing-coil 42 which is connected between each secondary winding of the excitation-transformer 4B and the two coupling-transformers 41 which energize the two ignitors 35 which are .to be excitedbythat winding of the excitation-transformer.

The primary windings of the excitation-transformers 40 are energized from an auxiliary threephase bus 43-, which -is.- energized from the secondary;windings--of an auxiliary transformer 44, the primary windings of which are connected to the main power-circuit 1 3.:

The fiIiHgPDOi-HBS, in the input-frequency cycles,are advanced or retarded by means of variably saturablereactors 45, which are connected in series with each of the three secondary windings oftheexcitation-transformer 40, the saturation of these reactors being controllable by means of a ,directecurrent saturating-coil 46;. which. is

excited from" a battery 41 through: a controllable:

rheostat 48'.

Duringea-ch:firing;half-cycle,.the voltage :de1-- livered. by. the :secondaryuwinding, of therEXcitH- tionrtransfzormer 40 is built; up -.:upon. an energy:

storing capacitor 49,,1jWhiChfiS connected .in'shunt acrQssthe: firing-excitation circuit; 7 To obtain a.

valve-action, afixed saturating reactor. 5m serially connected between the capaciton rand the two ignitor-coupling; transformers 24 I; which are served from that-circuit: Atapredetermined point: in :the half -cycle,. this, saturating reactor 50,: becomes saturated; thus suddenly losingiits. im-

pedance, andipermitting a heavy 'cu'rrentdmpulse to be discharged from the-capacitor.'intodthe;

ignitor-couplin'g transformers 4 Iii The secondary windinglof each :ignitor-coupling transformer 4| delivers only the positive peaks of. its; current to the .ignitor, 3 5. of. the .associated one ofthe-mainitubes; I to;'6,r-, this actioni'being accomplished .:by meansvv of a serially iconnected rectifier 5!;1A returnepathizforithe flux-decay current of ithe coupling=trhnsformer 4b :is provided in aknown mannerxbyrmeansxof La rectiher 52' which is connected. across the transformer secondary:

Since my converter is convertingnfrom a relativelydow frequcncytto; a:.relativtely highufre quency;. each; lowefrequency conducting-period, of each tube," must. be: brokeniup intcna plurality of :conductingrand; non-conducting periods, at

the high-frequency rate.

As more particularly described:andcla'imedin my copending application; the. grids Hand 34,! of

eachiofthe converter-tubes! tors; are utilized toalternately; block" and gzrelea'se the. firing of the: severaltubes, at the output-frequency rate. The two grids 3S and 34 of eachztube are energized together; from..the. same: high=frequency source, through'separate, serially connected resistors 53 and- 54.,fiso that: thetwo igridsican assume different potentialsacconding.=totheamount The grid-control circuits also include negative biasing-batteries 58 and 59 respectively, one biasing-battery 58 being for one group of converter tubes, l, 2 and 3, while the other biasing-battery 59 is for the other group 4, 5 and 6. Since each of the two groups of converter-tubes has its own cathode-circuit It or ll, which is common to all of the tubes of that group, the grids 33 and 34 of all of the tubes of each group can be energized from the same high-frequency source. Thus, the grids of the tubes I, 2 and 3 are ener gized from the high-frequency output-winding 56, in series with the negative biasing-battery 58; while the grids of the tubes 4, 5 and 5 are energized from the high-frequenc output-winding 5'1, in series with the negative biasing-battery 59. In an illustrative case, a negative bias of about 100 volts has been found advisable, for the batteries 58 and 59, in combination with a peak oscillator-voltage of about 200 volts, on each of the oscillator output-windings 56 and 5'1, although it is to be understood that I am not limited to any particular voltages.

Since the ignitor 35 of each of the convertertubes is energized only once during each inputfrequency cycle, and since the period during which an energizing current flows in the ignitor is only a brief portion of the input-irequency cycle, it will be obvious that the length of the portion of the input-frequency cycle during which any converter-tube could be fired, by the control-action of the grids, at the high-frequency rate, would be limited to the same brief portion of the low-frequency cycle as the duration of the flow of effective ignitor-current, if suitable means were not provided. I therefore utilize an auxiliary anode 35, in each tube; but contrary to ordinary practice, I usually or frequently find it desirable to provide for a Wide phase-shift adjustment of the firing-angle, as by means of the rheostat 43. To make this possible, as described and claimed in my copending application, I so excite the auxiliary anode 3b, in Fig. l, as to maintain a strong holding-arc thereon for 120 input-frequency degrees, plus the inputfrequency commutating-angle of the tubes, which may be another or 20 degrees, more or less.

Thus, in Fig. 1, the auxiliary electrodes 36 oi the six converter-tubes l to 5 are energized from a set of single-phase holding-circuit transformers 60. The three primary windings of the holding circuit transformers are energized from the auxiliary three-phase input-frequency bus 43. Each of the three holding-circuit transformers 60 has a plurality of secondary windings; and these secondary windings are illustrated as being connected in two zig-zag winding-connections 64 and 65, having neutral points 86 and 62', which are connected to the respective cathode-buses l6 and IT. The several phase-terminals of the zigzag winding 64 are utilized to energize the auxiliary anodes 36 of the converter-tubes I, 2 and 3, through separate current-limiting resistors 68, while the several phase-terminals of the zigzag winding 65 are utilized to energize the auxiliary anodes 36 of the converter-tubes i, 5 andB, each through its own resistor 68.

In order to obtain an auxiliary-anode energization-period of 120 input-frequency degrees, or more, for each of the converter-tubes l to 6, each tube has its auxiliary-anode 3t energized, not only from the usual phase-circuit, or terminal, of the holding-circuit transformer 60, but also, in parallel therewith, from the next lagging phase-circuit, as shown, for example, at 69. The

auxiliary-anode energization-circuits include rectifiers 70, which are connected, in each circuit, in series with each of the phase-terminals of the secondary windings 64 and 65, so as to avoid short-circuiting the parallel-connected windings, while at thesame time delivering only the positive impulses of current from the respective windings.

In the operation of the converting apparatus which is shown in Fig. 1, it may be noted that, although the main converter-tubes l to 6 are of a type in which neither the two grids 33 and 34 together, nor the ignitor 35, nor the auxiliary anode 36, is capable, in general, of interrupting the flow of a main-circuit current in any tube, once the tube has been fired by establishing an are between the main anode and the cathode, within the tube, nevertheless a load-circuit is provided, which is of such character as to be able to effect a periodic interruption of the tubecurrent, or of the main are within the tube, at the output-frequency rate. In the circuit which is shown in Fig. 1, this current-interrupting or commutating function is performed principally by the parallel-connected capacitor 30.

In the control-circuits, it is to be noted that each of the main converter-tubes I to 6 is fired once, during each input-frequency cycle, by the energization of its ignitor-circuit. When the ingltor 35 of any tube establishes a firing-arc, the auxiliary anode 36 of that tube practically instantly fires, and picks up a holding are, which is maintained for input-frequency degrees, plus the input-frequency commutating-time of the tubes, or for any other desired or necessary length of time. The commutating-time of the tubes is the time necessary to transfer the main are from one input-phase to another, and this commutating time can be shortened by utilizing a main transformer 8 which has a low reactance, and by other means.

While the grids 33 and 34 can not, in general, interrupt the main 'arc in their tube, once said main arc has been established, they can prevent the establishment of the main arc, if the grids are suiliciently negative with respect to the oathode of the tube, or if the control-grid 33 has a potential which is more negative than a certain critical potential. It is to be noted that the grids 33 and 34 of each tube are governed by a combination of a negative bias and a singlephase high-frequency voltage, so that, during a portion of each high-frequency cycle, the grids are sufiicientlynegative to block the firing or initiation of the main arc in the tube, after which the grids become sufliciently positive, at a predetermined point in each high-frequency cycle, to permit the firing of the tube, provided that an exciting-arc is being carried, either by the ignitor 35 or by the auxiliary electrode 36, and provided, also, that the main anode of the tube is sufilciently positive with respect to the tubecathode, at the moment.

It is to be noted that the grids of the tubes of one group of converter-tubes, namely the tubes I, 2 and 3, become sufficiently positive, so as to release the respective tubes, for firing, during positive half-cycles of the output-frequency, while the grids of the tubes of the other group, 4, 5 and 6, release their tubes during the negative half-cycles of the output-frequency. Thus, one or more tubes of one group is carrying current during one half-cycle of the output-frequency, while noneof the tubes of the other group are carrying current, the circuit being completed through the direct current: connection 2'2 -23;:

The. zig-zag .zconnection of 1 the .maimtransformer. secondaries l preventsi this .direct. curr.ent. from..

saturating the transformer.

During the nexthig-h-frequency halfi-icycle thei first: group of tubes. isnon-conducting;lwhil ethev second tube-group is.conducting..current.i

During this interchange, when power is being supplied alternately .by .the ncathode-Lbus :16 and by the cathode-bus..l1,?at the, high-frequency rate,:: the parallel-connected capacitor 3091s alternatelyi charging .and discharging; firstiin one directiona and then=inthe other, cooperating withthe; die. rest-current .returnecircuit path1'.22t--23. ':-to-.also:i provide a return-path for. whichever: tube-group;

is. carrying current at.v the. moment,:..whi1e; also. performing the function :of interruptlngthehighe.

frequency current when the other. tube-group \is' released, during any halt-cycle; ofs the highzoroutput -frequency.

Fig. 2shows a modification-of'the. power cire' I cuit in whicha six-phase converte'r operation is utilized; I utilize asix-phasesupplygobtained from the star-connected. six-phase secondarywinding H of a power-transformer.1%, thaving a three-phase delta-connected primarywinding .1 3

which is energized. fromwthethree-phasei-come.

menial-frequency. power-lines l3;-

There are twelve tubes .T'l'to T124; comprising. two groups having the. separate. cathode-buses. Theatubes TI to T6 LCOnStitutG-LtheEI l6 and IT. firstugroup, having. their anode-leads...l.4="connected to the respective phases'ot. the-six phase. supply-transformer windingfllt. Thetubes T1 to .IIZ constitute the second group; havingzthein anode. circuits? l4: alsoconnected to.thez.respec.-.

tive .phases of the. six phasesecondary .wind-in'g; Thus, one. secondary terminal is: connected; to the anode-:circuits: I 4: of 1 the tubes? Ti "and .T1 of-the first and second groups,-respectively.- Thenext lagging transformer-phase. istzconnected Ito.

the anode-circuits. I4 oiithe tubes: T2. .land.;.T8, respectively; and soioni. Allzof the C8thOdErCiricuitsr-l5'of the tubes'Il to TB of the-firstigrou-p. are connected to the cathode-bus; 15, 4 while: alli of. the cathode-circuits; I5;of.wthe tubes .T1 to.

T12v are connectedto the' c'athode.-bus .11..

The load-circuit, in Fig. 2, is connected Ito-the:-

two' cathode-buses l6,- and IT, respectively; the,

same; asin Fig. 1, except'thattheprimary-side load-circuitcapacitor 30.:of Fig; lhasibeeniomittedw in Fig. .2, byway of illustration .ofithe-r fact that itsfunction can betakenrover by utilizinga larger."

secondary-circuit capacitor 31; in parallehwith the load...

The. .controlecircuits; in. 2 .are essentially theusameuas in Fig. ,1, sonthat no; .further' explaa nation is considered necessary;- except: to note.

groups, aseinFig- Lathe secondary windings-of" the: .ignitor-coupling. insulatingetransformers: 4' h, and also the secondary windings ofuthe holdinge.

circuitatransformers: 80;..arer mid-tapped wind-i.-

ings, each .servingtwo diametrically. opposite ig-..

nitors or auxiliary anodes, ast-the "case. maynbep asv will be readil-y understood;

In Fig. 2, 1 also,:.- theholding-circuits. are are. ranged -so that each iauxiliary anode is:energized from-only onephase of the holding-circuit transformers 6 0, and: the holding-circuit: rectifiers 68 Or -Fig. 1 have been omitted: as being therefore unnecessary.- in Fig.2; which will notremain energized as long asthe holding-circuit in Fig. 1, whichmeans-that t yst m of 'Fig. 2 will not be susceptible .of as.

wideia rangeiofivoltage-regulation, by manipula tioni'of the:saturating-reactor rheostat 48, asis. possible: iniFig. 1.- The particular applicationafo'rwhich Fig. "2 .wasdesigned didnot require the additional. range of voltage-regulation.

While I have illustrated'my. invention in two different; forms; of embodiment, ancbwhile I have described the. same inzaccordance with: my best present: understanding, I wish it to beunderstood thataI am not limitedto the illustratedembodie men-ts or. to theexplanationswhichI have given; I desiregtherefore, that theappended claims shall be accorded the broadest construction consistentwith theirzlanguage;

I claim as my invention:

1. In combination, analternating-current-supply-circuit winding having a neutral point; means for: providing an alternating-current outputcircuit, the output-circuit having a frequency higher 'thanthe supply-circuit; a -multi-tube electronic converter between said supply circuit" winding and saidoutput-circuit, said converter having two groupsoftubes, each group having a :separate cathode-circuit output-bus; a mid tapped output transformer winding connected across-the two cathode-buses; and means for connecting thehmidpoint of the output-transformer to theneutraloi the'supply-cir'cuitwinding.

2; In combination, means for providing a supply-circuit having. a neutral point; means forv providing=-a high-frequency output-circuit? a multi-tube electronic converter. between said suppl y cir'cuit and said output-circuit, each tube of -.the-conve1=ter having a main anode-cathodecircui-t; andcontrol-electrode means, said controlelectrode. means being, in 1 general, incapableof interruptingthe currentdn the main -anode-cathode-circuit oif the-tubeg once said tube-has been firedg= saidconverter 1 comprising control-means for soenergizingcthe control-electrodemeans of each tube-as to intermittently block and unblock thefiring,..-at the output-frequency rate; said converterhaving two groups of tubes, each grouphaving. a separatecathode circuitoutput-bus,

the-output-frequency controls of the two tube-'- groups -being in phasempposition; a mid-tapped output-transformer winding connected across th'e two cathode-buses; and means for connecting the midpoint'of the output-transformer to the neu-- tral-of the sup.pl-y-circuit.

3. In combination; an alternating-current .sup-

p1y-circuit winding: having a neutral point ;'means for providing an- 1 alternating-currentoutput-circuit, the output-cirouit'hav-ing a frequency higher 1 than the supply circuitg a multi-tubeelectronic' converter between said supply-circuitwinding andsaid: output-circuit,-each tube of the converter having a main anode cathOde circuit,- 1 and control-electrode means, said contro1-electrode means being, in general, incapable of interrupting. "the; current in the. main anode-cathode circuit-of. thetube, once-said tube has been fired;

saidi.converter. comprising control-means fo so energizing the .controlz-electrode means of each.

tube asptocontinuously tend to. fire the tube during-.e, considerable: :portionxzof each positive half cyclelsof. .the: inputepower; and. to intermittently:

block and .unblock' such firing. at the output-fre- This producesa holding-circuit;-

quency rate; said converter having two groups of tubes, each group having a separate cathodecircuit output bus, the output-frequency controls of the two tube-groups being in phase-opposition a mid-tapped output-transformer winding connected across the two cathode-buses; and means for connecting the midpoint of the output-transformer to the neutral of the supply-circuit windmg.

4. In combination, an alternating-current supply-circuit winding having a neutral point; means for providing an alternating-current output-circuit, the output-circuit having a frequency higher than the supply-circuit; a multi-ignitron converter therebetween, each ignitron of the converter having a main anode-cathode circuit, an ignitor, an auxiliary anode, and grid-means; said converter comprising a control-means for each ignitron, including means for exciting the ignitor at the input-frequency, means for exciting the auxiliary anode so as to thereafter maintain a holding-arc for a considerable portion of an input-frequency cycle, and means for controlling the grid-means so as to alternately block and permit the firing of the ignitron on alternate halfcycles of the output-frequency; said converter having two groups of ignitrons, each group having a separate cathode-circuit output-bus, the output-frequency controls of the two ignitron-groups being in phase-opposition; a mid-tapped output transformer winding connected across the two cathode-buses; and means for connecting the midpoint of the output-transformer to the neutral of the supply-circuit winding.

5. In combination, an alternating-current supply-circuit winding having a neutral point; means for providing an alternating-current output-circuit, the output-circuit having a frequency higher than the supply-circuit; a multi-tube electronic converter between said supply-circuit winding and said output-circuit, said converter having two groups of tubes, each group having a separate cathode-circuit output-bus; a midtapped output-transformer winding connected across the two cathode-buses; means for connecting the midpoint of the output-transformer to the neutral of the supply-circuit winding, and a commutating-capacitor means, associated with the output-circuit, for materially assisting in commutating the successive half-cycles of the output-current.

6. In combination, means for providing a supply-circuit having a neutral point; means for providing a high-frequency output-circuit; a multi-tube electronic converter between said supply-circuit and said output-circuit, each tube of the converter having a main anode-cathode circuit, and control-electrode means, said controlelectrode means being, in general, incapable of interrupting the current in the main anodecathode circuit of the tube, once said tube has been fired; said converter comprising controlmeans for so energizing the control-electrode means of each tube as to intermittently block and unblock the firing, at the output-frequency rate; said converter having two groups of tubes, each group having a separate cathode-circuit output-bus, the output-frequency controls of the two tube-groups being in phase-opposition; a midtapped output transformer winding connected across the two cathode-busesfmeans for connecting the midpoint of the output-transformer to the neutral of the supply-circuit, and a commutating-capacitor means, associated with the output-circuit, for materially assisting in com- 10 mutating the successive half-cycles of the outputcurrent.

7. In combination, an alternating-current supply-circuit winding having a neutral point; means for providing an alternating-current outputcircuit, the output-circuit having a frequency higher than the supply-circuit; a multi-tube electronic converter between said supply-circuit winding and said output-circuit, each tube of the converter having a main anode-cathode circuit, and control-electrode means, said control-electrode means being, in general, incapable of interrupting the current in the main anode-cathode circuit of the tube, once said tube has been fired; said converter comprising control-means for so energizing the control-electrode means of each tube as to continuously tend to fire the tube durin a considerable portion of each positive halfcycle of the input-power, and to intermittently block and unblock such firing at the output-freuency rate; said converter having two groups of tubes, each group having a separate cathodecircuit output-bus, the output-frequency controls of the two tube-groups being in phaseopposition; a mid-tapped output-transformer winding connected across the two cathode-buses; means for connecting the midpoint of the outputtransformer to the neutral of the supply-circuit winding, and a commutating-capaci-tor means, associated with the output-circuit, for materially assisting in commutating the successive halfcycles of the output-current.

8. In combination, an alternating-current supply-circuit Winding having a neutral point; means for providing an alternating-current output-circuit, the output-circuit having a frequency higher than the supply-circuit; a multiignitron converter therebetween, each ignitron of the converter having a main anode-cathode circuit, an ignitor, an auxiliary anode, and gridmeans; said converter comprising a controlmeans for each ignitron, including means for exciting the ignitor at the input-frequency, means for exciting the auxiliary anode so as to thereafter maintain a holding-arc for a considerable portion of an input-frequency cycle, and means for controlling the grid-means so as to alternately block and permit the firing of the ignitron on alternate half-cycles of the output-frequency; said converter having two groups of ignitrons, each group having a separate cathode-circuit output-bus, the output-frequency controls of the two ignitron-groups being in phase-opposition; a mid-tapped output-transformer winding connected across the two cathode-buses; means for connecting the midpoint of the eutput transformer to the neutral of the supply-circuit winding, and a commutating-capacitor means, associated with the output-circuit, for materially assisting in commutating the successive half-cycles of the outputcurrent.

ii. In combination, an alternating-current supply-circuit winding having a neutral point; means for providing an alternatingwurrent output circuit, the output-circuit having a frequency higher than the supply-circuit; a multi-tube electronic converter between said supply-circuit winding and said output-circuit, said converter having two groups of tubes, each group having a separate cathode circuit output bus; a midtapped output-transformer Winding connected across the two cathode-buses; means for connecting the midpoint of the output-transformer to the neutral of the supply-circuit winding, a ccmmutating capacitor, connected in parallel- ECiICHit'JlEIQrtiOIL :to :said; output-itransformer winding, for materially assisting in commutating :the successive) half acyclesrot zthe. output current.

510. .In "combination;:means "forrproviding asupmouthodercircuitof ElJhGlillbQiiQl'lCB. said tube has 'l-beenilfired; :rsaidyconverter comprising controlstwo tube-groups being'in; phase-opposition; a tmidi-xtappedc'output a transformer winding con- -.:nected:lacr.oss thetwo -.cathode+buses;:means. for u connecting 113116 :midpoint -Poi the output-transiiiormerp-zto zthenneutral oi-ithe supply-circuit, a

.' comzmutatingacapacitor, z-aconnected in parallelcircuit-relation to :saidoutput-transformer wind- ;ing; lfortzmateri'ally assisting :incommutating the successive; .halficycles ofiithe: outpu-t current.

1. lliln 's cornbinia'tion, aan a1ternating-current rsupplyecircuit winding:.havingz.-a= neutral :point; means for providing amalternating-current' out- :put-circuit; .the output-circuit-havinga fre- ;qnency higher than :the supply-circuit; .a multi- .:tubecelectronic converter between said -supply-. zcircuit winding and:saidoutput-circuit,- each tube f ;the converter having: a main anode-cathode ::circuit, and control-electrode means, saidconltrol electrode means .being, 1 in general, incapable of interrupting thecurrent in the-main anodecathode. circuit/ofthe tube,--lonce said tube has -been: fired: said converter comprisingcontrolwmeans: for .:so-' energizing the control-electrode means-ofa each tube as to continuously tend to :fflTe' the: tube during a 1-considerable-portion of -12 each positive 1half-cyclerof, the. input-power, and to intermittently block: and I unblock such- :firing at \the output-frequency rate; said'converterwhaving two-groups of' tubes, each group-having a separate cathode-circuit: outpub bus; 'the outputfrequency controls of :the two tube-groups being 'in phase-opposition a mid-tapped output transformer Winding'connected across :the two cathode-buses; means for connecting the midpoint of the output-transformer tothe neutral of the supply circuit Winding, a commutating. capacitor, "COHIIGCtGdIlI'l :paral-lel cirouit relation to said outputetransform'er winding; ior-materia1ly ;;assistin in commutating -:the. successive half-cycles of the output-current.

.12;- In combination, an alternating-current supply-circuit winding having" a neutral: point;

means -i or providing: an alternating-current output-circuit, the output-circuit having -a frequency higherthan the supply-circuit; mmultiignitronconvcrter therebetween, "each ignitmn' of the 'converterhaving almain anode cathode 'circuit, anaignitor, :an: auxiliary" anode, :and gridmeans; 'said 'converiter --comprising a controlmeans for each'ignitron; lincludingfmeansifor exciting :the ignitor at the input-irequencymeans forcxciting the auxiliary anode rsoas toitherieaf ter 'maintain .a holding-arc ior a considerable: portion of antinput-ifrequencyr cycle;; and means for controlling'ithe 'grid-means'zi'so-r as" to s alternately block and permit :thezzfiringl of. =theignitron aon 1 alternate "t half cycles :of the "output-frequency; said: converter: having: two -groups ofrsignitrons, each group havingxa separatescathodeacircuit output-busgthe output-frequencycontrols of the two ignitron'egroupsw being in :phaseJ-opposition;

a mid-tapped output -transformer winding." connested. across: the two 'zcathode-buses;=-a-rmeans for connecting thezmidpoint' of the output-transformer to the neutral of =the supplyrcircuit'wind- -ing;1 a commutating-capacitor, connectedimparallel-circnit relation' ito said-output-ztransformer 2 winding; forrmateriallyassisting: in commutating the successive. half -cyoles of the: output current.

z-JOHNL; BOYER. 

